Effective interspecies electron transfer (IET) is key to the efficient functioning of anaerobic microbial communities. On the other hand, even today there is little information on the mechanisms by which microorganisms cooperate to exchange electrons. Direct interspecies electron transfer (DIET) is a metabolic pathway of IET in which free electrons flow from one microorganism to another without being transported by reduced molecules such as molecular hydrogen or formate. This pathway has been proposed as being present between fermentative and methanogenic populations in the granule during anaerobic digestion. It would involve the extracellular polymeric substances (EPS) of the granule to facilitate the transfer of free electrons. The present study examines these hypotheses. The DIET is divided into two broad categories, DIET mediated by a conductive non-organic material (mDIET) and the biological DIET (bDIET). The latter only involves the cells themselves and their components (pilis, nanowires, etc.). Using anaerobic granules in which Geobacter was not dominant (Geobacter is known for its frequent participation in DIET), the tests carried out with two co-substrates showed that the methanogenic activities of the formate and the hydrogen decreased in the presence of a non-methanogenic co-substrate such as ethanol. This may indicate that the bDIET occurs and competes with hydrogen and formate. In addition, the addition of conductive microparticles, such as stainless steel and granular activated carbon, increases the methanogenic activity in the disintegrated granules as compared to the disintegrated granules without microparticles. These results indicate that syntrophic bacteria from anaerobic sludge, excluding Geobacter species, can also perform mDIET. On the other hand, further to tests with a small reactor designed for the study of mDIET, it was determined that this mechanism may not be exclusive, i.e. alone it can not ensure the survival and growth of the methanogens carrying it out; other IET mechanisms may have to occur in parallel with the mDIET. Acetoclast methanogens, known to perform bDIET, have been enriched in the mDIET assays, as well as some non-acetoclastic methanogens, suggesting a role that is still undefined to date in this pathway. Finally, further to studies of granule EPS, the Methanosaeta concilii proteins were shown to be best represented in all three granular sludges studied, highlighting its role in the formation and maintenance of the anaerobic granule, as well as its stability and effectiveness. Without confirming a specific role for EPS, this study highlights the existence of structures and molecules in the extracellular matrix of the granule that chemically have the ability to participate in the bDIET, such as humic substances and formate dehydrogenases.